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Class 10MathematicsArithmetic Progressions (AP)Word problems based on APsEasy
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A staircase has (50) tiles in the bottom row and (4) fewer tiles in each upper row. How many tiles are there in (9) rows?

Answer and explanation

Correct answer: 306

The numbers of tiles form a decreasing AP: 50, 46, 42, \ldots Here, \(a=50\), \(d=-4\), and \(n=9\). Therefore, \(S_9=\frac{9}{2}[2(50)+8(-4)]=\frac{9}{2}(68)=306\). Hence, the correct answer is 306. A value such as 316 can result from using the decrease or the number of terms incorrectly. Exam tip: always use a negative common difference for a decreasing AP.

Related tags

Arithmetic ProgressionAp Word ProblemsDecreasing ApSum Of N TermsClass 10 MathematicsWord Problems Based On ApsArithmetic Progressions (Ap)Arithmetic Progressions Ap
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